1. Field of the Invention
The present invention relates to the manufacture of plastic bags or packages having two plies of thermoplastic sheeting, both plies having closure strips formed or included on their facing inner edges so as to form a sliderless zipper closure for the openings of the bags or packages made therefrom. The plies may be formed of two separate sheets or a single sheet folded over.
2. Description of the Prior Art
The present invention relates to improvements in the package-making art and may be practiced, without limitation, in the manufacture of thermoplastic bags and trays of the kind that may be used for various consumer products, but which are particularly useful for food products which must be kept in moisture and air-tight packages, free from leakage until opened for access to the product contents, which packages are then reclosable by zipper means to protect any remainder of the product therein.
The indicated art is fairly well developed, but nevertheless is still susceptible of improvements contributing to increased efficiency and cost effectiveness.
One problem that still exists in the production of packages from continuous zipper-equipped sheet material, is the difficulty in attaining a satisfactory sealing of the bag or package against leakage, where the zipper and area of film engaged by the zipper extends through the side seal areas separating one bag or package from the next.